Problematic substance use is widespread in many American Indian communities, and early adolescence is a critical period for the development of subsequent substance problems. Efforts to prevent early substance abuse are ongoing on many reservations but often are not informed by scientific evidence of effectiveness - largely because such evidence is sorely lacking. We propose to partner with a reservation community with high rates of substance problems to adapt, implement, and rigorously evaluate a program designed to prevent early initiation of substance use and the myriad of problems that accompany early use. The identification of early substance use as a target and the selection of the particular intervention approach we propose have directly resulted from a longstanding university-tribal community relationship and, in particular, from community input within the context of two recent projects funded by NIDA (RC4DA029974, Whitesell & Beals, PIs; and R01DA027665, Whitesell, PI). A clear message arising out of both projects has been the need to engage families and culture in the prevention of early onset substance use. In this project, we will continue this partnership to translate a rigorously evaluated evidence-based practice for use with tribal families, adapting and anchoring it within a cultural practice arising from within the community. We will draw on the strengths of both university and community partners, implementing innovative intervention development methods within a community collaborative research and evaluation context. We will address three specific aims: 1. Develop a culturally grounded, family-based early substance use prevention intervention tailored to a Northern Plains American Indian Reservation. Use an evidence-based practice approach to implement a proven program (Iowa Strengthening Families Program/ISFP) within a new context, working with community partners to translate ISFP for the local context, including deep and meaningful adaptations in how the curricular content is delivered. Use a practice-based evidence approach to integrate a cultural curriculum (Seven Directions/SD) developed within the community into the ISFP curriculum, drawing on local knowledge of effective practices to further ground substance use prevention efforts within the cultural context. 2. Pilot the adapted Seven Directions for Stronger Families (SDSF) program to determine feasibility, refine details, and maximize fit within the community. 3. Use the principles of the Multiphase Optimization Strategy (MOST) for intervention evaluation and development, to determine the relative effect size of different intervention components and inform a final SDSF program that balances effectiveness and efficiency. 4. Set the stage for broad implementation of SDSF by the tribal health administration and a randomized controlled trial of the full intervention.